Safety inspection is of great significance in the fields of anti-terrorism, cracking down on drug trafficking and smuggling, etc. After the U.S. September 11th event, more and more attention is paid to safety inspection all over the world, and especially at public locations such as airports, stations, customs, and dock, etc., a series of safety inspection measures is taken to perform a strict inspection on passengers' baggage and articles, cargo container, etc.
Currently, a predominant imaging technology employed by a widely used safety inspection system is radiation imaging technology. According to the principle of rays' exponential decay, the radiation imaging technology adopts a system in which a ray source irradiates an object under examination on one side of the object under examination, and a ray collecting arrangement receives the rays after they have passed through the object under examination. The ray collecting arrangement converts the received rays into a digital signal and outputs the digital signal to a computer for imaging. The computer processes the collected data, synthesizes or reconstructs an image, and displays the image. A safety inspection system employing the radiation imaging technology is capable of performing tomography or perspective imaging. Tomography illustrates tomographic images of an object under examination and can combine multiple layers of tomographic images into a three-dimensional (3D) stereo image. Perspective imaging illustrates a two-dimensional (2D) perspective image of an object under examination.
A tomography safety inspection system generally requires a computed tomography (CT) device, where at least one of the object under examination and the ray sources are capable of being rotated, since tomography requires the ray collecting arrangement to receive omnidirectional irradiation of the object under examination to obtain transmissive projection data of the ray beam. In a practical application, it is generally required for the safety inspection system to inspect on-line in real time, requiring a very high imaging speed of the safety inspection system. For inspection of civil aviation articles, for example, since the customs affair rate is required not to be more than 0.5 meters per second, it is very difficult for even the helical CT device with a large pitch to meet the requirement. Furthermore, for a large object such as a customs container, it is very difficult to rotate the container or the ray source. In addition, the cost of the CT device is very high. Because of these factors, the safety inspection system that performs stereo imaging with the CT device is not widely used.
Compared to the tomography safety inspection system, a perspective imaging safety inspection system is widely used in public locations such as airports, stations, customs and dock, etc. However, the perspective imaging safety inspection system cannot avoid an overlap effect of an object in the ray direction and solve the overlap problem of an object in the ray direction, resulting in the fact that the performance of the perspective imaging safety inspection system is considerably low.
A single-segment and multi-segment linear track scanning imaging mode is proposed in U.S. Patent Application Publication Nos. 2070116177, 20070116175 (which issued as U.S. Pat. No. 7,424,089), and 20080075226 (which issued as U.S. Pat. No. 7,499,522); which correspond respectively to Chinese Patent Application Nos. 200510123587.6 (published as Chinese Patent Application Publication No. 1971414), 200510123588.0 (published as Chinese Patent Application Publication No. 1971620), and 200610076573.8 (published as Chinese Patent Application Publication No. 101071109), all of which are incorporated by reference in their entireties, where, in the course of scanning, an object to be examined, located between a ray source and an array of detectors, is made to move linearly relative to the ray source and the array of detectors (the field angle formed by the ray source and the array of detectors is the scanning viewing angle when imaging), and there is no relative rotation between the ray source and the array of detectors and the object, which may substantially meet the requirement of fast imaging of the safety inspection system and solve the problems that it is difficult to rotate a large object and that there is object overlap in the ray direction of the perspective imaging safety inspection system. In multi-segment linear track scanning imaging, the travel track of an object under examination includes at least two segments of linear tracks having an angle between one another; and the object under examination only performs translational movement in the at least two segments of linear tracks with no rotation at all. The multi-segment linear track scanning imaging mode may enlarge the scanning viewing angle of the system by multiple times (depending on the number of the segments of linear tracks and the number of arrays of detectors) by irradiating the object under examination multiple times with the same ray source through the use of a plurality of arrays of detectors arranged in the multi-segment linear tracks, and may thus solve the problem of limited angle projection existing in the practical application of a single segment. However, there is a common disadvantage among the above-mentioned imaging systems: in order to cause the detector and the ray source to form a sufficiently large scanning viewing angle to achieve a high quality image, the detector should cover a sufficiently long range in the movement direction of the object, thereby resulting in a high cost of the detector in the imaging system and a long scanning distance of the examined object.